SEOUL, SOUTH KOREA (AP) - Investigators have detained a South Korean army private suspected in a grenade blast that injured five of his fellow soldiers at a border post near the tense border with North Korea, an army official said Thursday.

The suspect, identified only by his family name Hwang, allegedly threw the hand grenade Sunday at a barrack on the grounds of the guard post, the official said.

The army official said final investigations were under way to find the exact cause of the attack, adding that military police planned to seek a warrant to formally arrest the suspect later in the day.

The official spoke on condition of anonymity because he was not authorized to speak to media.

Meanwhile, Yonhap news agency reported Hwang confessed to his crime to army investigators after being detained late Wednesday. Yonhap also reported he had difficulties serving at a front-line unit.

The army official said he could not immediately confirm the Yonhap report.

In 2005, a South Korean soldier tossed a hand grenade and opened fire at a front-line army unit in a shooting rampage that left eight colleagues dead and several others injured.

The incident raised serious questions about the level of discipline in South Korea’s 680,000-member military. All able-bodied South Korean men must serve about two years in the military under a conscription system aimed at deterring aggression from North Korea.